1. Field of the Invention
The present invention relates to a weld-position detector used with an automatic welding machine, e.g., a robot welding machine having an end-effector on which a welding torch is mounted. More particularly, the present invention relates to a weld-position detector, for detecting a weld-position with high accuracy using a laser beam, provided with an optical axis adjustment means for adjusting the optical axis of the laser beam.
2. Description of the Related Art
It is known to use a robot welding machine, such as a arc-welding position multi-articulated welding robot, for automatically welding a workpiece. When a multi-articulated welding robot is used for carrying out automatic welding of a workpiece according to a predetermined welding program stored in a robot control unit, the distal end of a welding torch on the welding robot must be continuously brought into alignment with the portion of the workpiece where the weld should be applied. Thus, the welding robot is always provided with a weld-position detector for detecting the position on the workpiece where the welding is to be implemented by the welding torch in advance of the application of the welding arc. The weld-position detector is attached to the end-effector of the welding robot in combination with the welding torch and sends detection signals, as feedback signals, to a robot control unit which corrects a misalignment of the end of the welding torch, from the weld position determined by the welding program, in response to the feedback signals. The weld-position detector includes a semiconductor laser unit for emitting a detection laser-beam, a reflecting mirror unit for reflecting the detection laser-beam, a galvanometer unit (a drive unit) for moving the reflecting mirror so as to permit the detection laser-beam to scan portions of the workpiece, a light-receiving unit for receiving the detection laser-beam reflected from portions of the workpiece and to focus the detection laser-beam onto a charge-coupled image sensor to thereby form an image of the scanned portion of the workpiece, the light-receiving unit further providing two-dimensional data of the scanned portions of the workpiece from the data in the image on the charge-coupled image sensor and information on the angle of the reflecting mirror. At this stage, the charge-coupled image sensor incorporated in the light-receiving unit of the conventional welded position detector consists of a single-dimension CCD device (i.e., a line CCD sensor) which has a plurality of array elements and is 10 through 20.mu. meters wide. Therefore, when the detection laser-beam scans the workpiece in response to the movement of the reflecting mirror driven by the galvanometer, it is necessary that the scanning plane in which the detection laser-beam carries out the scanning motion due to the movement of the mirror is in alignment with a reflecting plane in which the detection laser-beam, after being reflected from the workpiece, moves along the charge-coupled image sensor. Namely, an exact alignment of the scanning plane of the detection laser-beam and the line CCD sensor is needed. Thus, the conventional weld-position detector must be finely adjusted to establish the above-mentioned alignment of the scanning plane of the detection laser-beam and the line CCD sensor by separately and delicately adjusting the positions of respective units and components on a fixture, or in the housing of the weld-position detector, during assembly of the respective units and components into the weld-position detector or after assembly of the weld-position detector.
Nevertheless, it is very difficult for an operator to accomplish the above-described alignment of the scanning plane of the detection laser-beam and the Line CCD sensor by finely adjusting the mounting positions of the respective units and components of the weld-position detector. Further, the difficulty in adjusting the mounting positions of the units and components makes the assembly and maintenance of the welded position detector cumbersome, and consequently, there was a limit to the performance of the weld-position detector. Namely, the conventional weld-position detector is not sufficiently accurate. Therefore, an improvement in the construction of the weld-position detector has been required.